Proteins are main constituents of a broad range of food products in powder form, from dairy to dough-based foods. Water is the main responsible of physical properties modifications in powders and many scientific studies have been focusing on characterizing the role of water content and water activity in carbohydrates powders. This work deals with the assessment of physical properties and dissolution behavior of milk proteins powders and their interactions with carbohydrates (lactose). In the first part, micellar caseins, native and denatured β-lactoglobulin and Na-caseinate powders were selected and equilibrated at different water activities. In the second part, binary mixtures of proteins with lactose were prepared in different proportions (25:75 and 75:25). Sorption isotherms were built at 25 °C and water adsorption kinetics was found to be faster in proteins than in carbohydrates. Thermal analysis (DSC) showed that micellar caseins and Na-caseinate exhibit a clear glass transition, while the measurement was not easy for BLG powders. In binary systems, proteins delayed lactose crystallization, up to a different extent depending on the kind of protein. Dissolution behavior was measured by conductimetry; the protein structure (native vs denatured) and its initial water activity played an important role, especially influencing powder's wettability. The presence of lactose strongly accelerated the dissolution process, in a more important way for BLG. Scientific findings could lead to improved powder engineering, in order to optimize dissolution behavior and storage stability of protein-based foods.